One way to eradicate tumors is to heat them while keeping the surrounding tissue cool. For this, metal nanoparticles are typically used because they accumulate in tumor sites and couple with laser light at a specific wavelength to act as thermal generators. However, laser beams quickly lose their intensity as they penetrate tissue, making it difficult to access deeper tissues with an external light source. Bagley et al. provide a possible solution by bringing the light source closer to tumor tissue with implantable devices.

The authors engineered several illumination devices that are attached to an external near-infrared laser source to be used in conjunction with intravascularly administered gold nanorods, which heat up when exposed to the light. The designs of candidate devices included silica rods with varying geometries and a fiber optic mesh encased in silicone. The researchers first evaluated the illumination efficiency of their device candidates with a computational model, which used an approximate model of a mouse abdomen with key organs defined by their optical properties, such as scattering and absorption coefficients. At the same time, they characterized the performance of their devices by using them to illuminate plain buffer solutions spiked with the gold nanorods. The results suggested that a 3-cm silica rod with a tapered edge produced the optimal illumination pattern and selective heating of nanorods in the target area. In order to assess the in vivo performance of the identified device, the authors implanted it in the abdominal cavity of an orthotopic mouse model of ovarian cancer. They used implanted thermocouples to show that the test animals exhibited more effective heating of their ovarian tumors, as well as the liver and intestine, as compared with that of controls without nanorods. Even though the temperature elevations in the liver and intestine were not desirable, histological examination confirmed that the tissue viability in those organs remained acceptable. In a separate experiment, the scientists also demonstrated that the local heating enhanced the tumors’ uptake of an anticancer drug, doxorubicin, as well as an imaging contrast agent, highlighting the extended functionality of their device.

The ability to access tumors at deeper and more complex anatomical locations with the implantable devices is highly promising for cancer treatment. However, one of the remaining challenges is to improve their selectivity and reduce the heating of healthy tissues that accumulate therapeutic nanoparticles.